1. Field of the Invention
The present invention relates to a device for driving the objective lens of an optical disc apparatus for optically recording or reading information on or from an information recording medium.
2. Description of the Related Art
Generally, to write or read information to or from an optical disc with accuracy by means of an optical disc apparatus, it is necessary to perform a focus control operation to control the distance between the objective lens and the optical disc with respect to any warp of the optical disc, and a tracking control operation to allow the objective lens to cope with any eccentricity in the information track on the optical disc. To perform these control operations, an optical disc apparatus is equipped with an objective lens driving device for moving the objective lens in the focusing and tracking directions.
The objective lens driving device includes a lens holder for supporting the objective lens. This lens holder is supported by a plurality of springs and is equipped with focusing coils and tracking coils. Attached to the base of the lens holder are magnets which are opposed to the focusing and tracking coils.
An example of such an objective lens driving device is disclosed in Japanese Patent Unexamined Publication No. 64-7344. The device disclosed has in its upper and lower sections a pair of mutually crossing connecting members connected at one end to the base of the device and at the other end to the lens holder, through the intermediation of an elastic joint. In this device, focus control is effected along an axis passing the center of gravity of a movable device section and extending in parallel with the optical axis of the objective lens, and tracking control is effected by rotating the movable device section around the above-mentioned axis. The movable device section is supported by a link mechanism in such a manner as to be only capable of the movements in the direction of and around the above-mentioned axis, which passes the center of gravity of the movable device section. Therefore, if it receives an inertial force at the time of access, the device does not undergo any vibration, so that the access time can be relatively short.
A problem with the above prior-art objective lens driving device is that it has an excessive height due to the crossing structure of the connecting members. Furthermore, a single connecting member is composed of five parts: the end portions, the link in the middle, and the elastic joint members. In addition to this large number of parts, this device requires a three-dimensional assembling operation, which is rather difficult to perform.